I. Field of the Invention
This invention relates generally to switches positioned over resilient steering-wheel airbags for activating automobile horns, and more particularly, to an improved, inexpensive membrane switch which requires a reduced amount of applied force to obtain a good electrical closure of the switch.
II. Discussion of the Prior Art
Automobile horns are typically located in the engine compartment, and are remotely controlled and activated by one or more switches positioned on the automobile steering wheel. These switches are typically provided at the center or hub of the steering wheel. Thus, they are conveniently located and accessible to the driver when honking the automobile horn is necessitated. Automobiles manufactured today are usually provided with a driver's side airbag, which will be a mandatory device shortly. This airbag is stored in the steering wheel hub, and is adapted to inflate quickly upon impact. Accordingly, the airbag cover needs to be resilient so that it won't obstruct proper inflation of the airbag. The switches implemented for activating the horn are required to attain a good electrical closure when only a moderate amount of force is applied to the switch. This specification is necessary so a driver does not need to struggle to honk the horn during an emergency, such as to avoid an accident, warn a child approaching the street, or frightening away animals along the roadside.
The engineering dilemma automotive manufacturers face is providing an effective horn switch across a resilient surface comprising an airbag assembly. This is because a firm supporting surface for the switch cannot be placed across the airbag assembly without creating a detriment to operation of the airbag assembly. Accordingly, the switch needs to be capable of providing a good electrical closure when placed across a resilient airbag assembly, even when only a moderate amount of force is applied thereon. Automotive manufacturers today are now requiring that as little as four pounds of force applied to the switch should create a good electrical closure of the switch. To date, meeting such a difficult requirement has necessitated designing complicated and expensive membrane switches to be placed across the resilient airbag surface.
U.S. Pat. No. 5,265,904 to Shelton et al. teaches an airbag cover with an integral horn switch. Alternating strips of positive and negative horn contacts are provided on the common inner surface of the outer horn cover. These strips are positioned over and opposed from a conductive layer positioned across the airbag. As the outer horn cover is depressed, the alternating strips of positive and negative horn contacts are electrically connected via the inner conductive layer, thus forming a closed switch. The inner and outer covers supporting the contact strips and the conductive layer are both resilient, wherein the inner cover is positioned across a resilient airbag. Accordingly, a relatively large force needs to be applied to the outer cover to cause the alternating contacts to each make a good electrical contact with the inner conductive layer.
U.S. Pat. No. 5,198,629 to Hayashi et al. teaches a steering wheel with a molded membrane switch positioned across a steering wheel airbag device. Referring to FIG. 3, a pair of switches are formed by three conductive layers sandwiching two layers of interlaced dielectric members. Closure of either of the membrane switches can be used to sound the horn. As shown in FIGS. 4 and 5, a plot pattern of insulator ink is defined on the outer contact members such that they are sandwiched between the contact members, and thus, serve as both insulators and pressure concentrating members. The inner conductive layer is manufactured free of any plot pattern, and can be brought into electrical contact with either of the outer conductive layers depending on where the external force us applied.
U.S. Pat. No. 5,085,462 to Gualtier teaches a membrane switch positioned across a steering wheel airbag module. The lower electrode is shown to include an upwardly projecting contact portion extending inwardly into a respective aperture of a foam insulator. A relatively large amount of force needs to be applied to bring the opposing electrodes into electrical contact with one another. In FIG. 13, the outer cover includes a plurality of downwardly projecting nodes which help reduce the required amount of pressure necessary to close the switch. However, in that these nodes are formed integral to the cover, and separate from the switch itself, extensive care needs to be taken that the nodes are precisely aligned above the upper electrode during final assembly. This alignment is tedious, time consuming and expensive since these nodes are not integral to one of the conductive layers.
Other steering wheel assemblies seen to include a membrane switch positioned across an airbag assembly are disclosed in U.S. Pat. Nos. 5,002,306 to Hiramitsu et al., and 4,934,735 to Embach. Each of these devices requires a relatively large amount of force to be applied to adequately bring the opposing electrodes into contact with one another to close a switch. Moreover, due to the positioning of the membrane switches, a driver needs to pay particular attention to the location of these switches, and cannot indiscriminently depress any portion of the steering wheel hub one chooses to activate the horn. This can be dangerous in times of an emergency, such as when one needs to immediately activate the horn without looking at the steering wheel to avoid an accident, or gain the attention of a child or animal. U.S. Pat. No. 4,714,806 to Nuiinui et al. teaches a tape switch assembly for use with an automobile steering wheel. This device includes a rigid bottom layer, and is not adapted to be positioned across an airbag or a resilient surface.
An improved membrane switch for an automobile horn which can be provided over a resilient airbag on a steering wheel is desirable. Such a switch should effectively close with a minimal amount of force applied thereto while positioned over a resilient surface, such as an airbag assembly.